Image heating apparatus with first and second elastic members

ABSTRACT

An image heating apparatus includes a first member; a second member for forming a nip in cooperation with the first member; a first frame for supporting the first frame a second frame connected to the first member frame rotation about a rotational axis; a first pressing member for pressing the second member toward the first member, away from the second frame; and a second pressing member for applying an additional pressure between the first and second frames so that an additional pressure is applied between the first and second member.

This application is a continuation of Application Ser. No. 08/193,556,filed Feb. 8, 1994, now abandoned.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image heating apparatus for heatinga recording material, in which the recording material is heated as it ispassed through a nip formed between a pair of pressing members beingpressed to each other.

In an image forming apparatus such as an electrophotographic copyingmachine, printer, or facsimile, an unfixed toner image is directlyformed or indirectly formed on (transferred to) a sheet of material(recording material) in a processing means for image formation, with theuse of an appropriate image forming principle and system, incorrespondence with the imaging data for a target image, and isthermally fixed by the heating apparatus. As the heating apparatusgenerally speaking, a thermal fixing apparatus of a heat roller type iscommonly used.

This heat roller type heating apparatus comprises a heat roller (fixingroller) as a rotary heating means, and a pressure roller as a rotaryopposing (pressing) means, which are pressed to each other by a pressingmeans, forming a fixing nip (pressure nip), where the sheet of materialcarrying the unfixed toner image is introduced as a member to be heated.As the sheet is passed through the nip, the unfixed toner image is fixedonto the sheet surface by the heat and pressure from the pair ofrollers.

The heat roller generally comprises a piece of aluminum pipe, which isthe main structure, in which a halogen heater, for example, ispositioned as a heating member. The power supply to the heating memberis controlled by a temperature controlling means in such a manner thatthe temperature of the main structure of the heat roller is maintainedat a predetermined high temperature, that is, a fixing temperature.

Generally speaking, as the pressure roller, a roller comprising an ironcore and a heat resistant rubber material layer formed over the ironcore is employed, and as a means for pressing the heat roller andpressure roller to each other, a pressure generating spring (compressioncoil spring) is used.

As the heat roller and pressure roller are pressed to each other, theheat resistant rubber material layer of the pressure roller deforms; asa result, a nip is formed in which the surface of the pressure rollercomes in contact with the surface of the heat roller. The width of thisnip (nip length in the rotational direction of the roller), along withthe heating temperature, is critical to guaranteeing the fixingperformance. In other words, how to maintain stably a sufficient nipwidth is one of the critical points in the apparatus design.

In the past, there was a method in which the positional relation betweenthe heat roller and pressure roller was fixed in consideration of thepredicted deformation of the rubber material layer of the pressureroller, and another method in which one of the pair of rollers was fixedbut the other was mounted on a pressure spring in such a manner that thecontact pressure between the pair of roller was adjusted in response tothe value calculated in advance based on the relation between thedisplacement of the spring and the resulting pressure. As far as thestability of the nip width or nip pressure is concerned, the latterusing the pressing means comprising the spring is superior in mostcases.

In recent years, the heating apparatus of a film heating type has cometo be put to practical use as the image fixing thermal apparatus. Thistype of heating apparatus has been disclosed in U.S. Pat. No. 149,941,U.S. Ser. Nos. 4444,802 and 712,532, and U.S. Pat. No. 5,148,226. Inthis type of heating apparatus, a heat resistant film is run between aheating means and an opposing (pressing) means, being sandwiched betweenthem, wherein a sheet of material carrying an unfixed toner image isintroduced, as the material to be heated, into a nip formed by theheating means and opposing means, with the heat resistant film beinginterposed, and while the sheet is passed through the nip, being firmlypressed on the heat resistant film, the heat from the heating means istransmitted to the sheet through the heat resistant film, fixingthermally the unfixed toner image onto the sheet surface.

The heating apparatus of such a through-film heating system can use aheating means with a low heating capacity and a thin heat resistantfilm, the temperatures of which quickly rise; therefore, it has suchadvantages that it can save electrical power, shorten the wait time(quick startup), reduce the temperature increase in the machine such asthe image forming apparatus, and also, it is very effective as theheating apparatus.

As the heating means, a so-called ceramic heater (slid-state heater),comprising basically a heat resistant and electrically insulatingceramic substrate and an exothermic resistive member, is used, and itgenerates heat as the electrical power is supplied to the resistor.

As the opposing means, a pressure roller like the one used in theheating apparatus of the aforementioned heat roller type, comprising aniron core and a heat resistant rubber layer, is used. As the pressingmeans for pressing the heater as the heating means and the pressureroller as the opposing means to each other, with the heat resistant filmbeing interposed, a means for pressing them with the use of a pressurespring is generally used in this case also.

Further, in the heating apparatus of this through-film heatingapparatus, the heat resistant rubber material layer of the pressureroller deforms due to the pressure generated by the heater and pressureroller pressed to each other with the heat resistant film beinginterposed, forming thereby a nip n which the surface of the pressureroller conforms to the contour of the heat roller, indirectly throughthe heat resistant film. The width of this nip is just as critical as itis in the heating apparatus of the heat roller type for guaranteeing thestable heating temperature and the stable fixing performance. In otherwords, to maintain stably the nip having a sufficient width and a properform is one of the critical points of the apparatus design.

Generally speaking, the pressure between the heating means and opposingmeans in the fixing apparatus as the heating apparatus such as the onedescribed above is rather large; for example, the overall pressure is 5to 10 kg in a small apparatus, and 40 to 60 kg in a large one. When theapparatus is jammed because the sheet of material to be heated haswrapped around the heating means or opposing means, or when the sheethas stuck in the pressure nip between the heating means and opposingmeans as the apparatus is suddenly stopped, the above-described pressureneeds to be released in order to handle the jam. However, in theapparatus using the prior pressure generating system, the abovementioned large pressure cannot be easily released, and in addition, thepressure releasing mechanism is complicated, making it costly, andrequires a large strength to operate the mechanism; therefore, it needsa lot of improvements in many ways.

SUMMARY OF THE INVENTION

Accordingly, the principle object of the present invention is to providean image heating apparatus which allows the pressure of the pressuregenerating spring to reduced.

Another object of the present invention is to provided an image heatingapparatus in which the force necessary to release the pressure isreduced.

According to an aspect of the present invention, the image heatingapparatus comprising a first member, a second member for forming a nipin cooperation with said first member, a first frame for supporting saidfirst member, a second frame attached to said first member in a mannerto rotate about an axis, a first pressing member for pressing saidsecond member toward said first member, away from said second frame, anda second pressing member for generating an additional pressure betweensaid first and second frame so that subsequent additional pressure isgenerated between said first and second member.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are a partially cutaway side view of an embodimentof the apparatus according to the present invention, and a partiallycutaway side view of the apparatus in a state in which the pressure hasbeen released.

FIG. 2 is a sectional view of the apparatus.

FIG. 3 is a rear view of the apparatus, with the middle portion beingomitted.

FIG. 4 is a longitudinal section of the rear portion of the apparatus,with the middle portion being omitted.

FIGS. 5(a) and 5(b) are a partially cutaway side view of the secondembodiment of the apparatus according to the present invention, and apartially cutaway side view of the apparatus in a state in which thepressure has been released.

FIG. 6 is a longitudinal section of the rear portion of the apparatuswith the middle portion being omitted.

FIGS. 7(a) and 7(b) are a sectional view of the third embodiment, and asectional view of the embodiment in a state in which the pressure hasbeen released.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 4 shows embodiments of the image heating apparatus accordingto the present invention. In the embodiments, the image heatingapparatus, that is, the fixing apparatus, is of a through-film heatingtype.

FIG. 1(a) is a partially cutaway side view of the apparatus; FIG. 1(b),a partially cutaway side view of the apparatus in a state in which thepressure has been released; FIG. 2, a sectional view of the apparatus;FIG. 3, a rear view of the apparatus with the middle portion beingomitted, and FIG. 4 is a longitudinal section of the rear portion of theapparatus with the middle portion being omitted.

A reference numeral 1 designates a frame of the apparatus; 2 and 2, leftand right side plates; and reference numerals 3 and 3 are guide groovescut to extend vertically in the left and right side plate, with theguide groove in the left plate being symmetrical to the one in the rightplate. The guides grooves 3 and 3 have open ends at the top surfaces ofthe respective side plates.

A reference numeral 4 designates a pressure roller as a means opposing aheating means, which comprises a metallic core 5 and a heat resistantrubber material layer 6. At the opposite ends of the metallic core 5,bearings 7 and 7 are attached. These bearings 7 and 7 are engaged intothe guide grooves 3 and 3 of the left and right plates 2 and 2 of theframe 1 through the open ends at the top, and are slid down to thebottom ends of the guide grooves, whereby the pressure roller 4 issuspended between the left and right side plates 2 and 2 of the frame 1being enabled to rotate freely by the bearings 7 and 7. A referencenumeral 8 designates a driving gear affixed to one end of the metalliccore 5 of the pressure roller 4.

A reference numeral 9 designates an internal film guide stay (guidingmember) shaped like a trough, the sectional area of which looks likehalf a circle, and 10 designates an integrally formed extension of thisguide stay 9. On the bottom facing surface of this guide stay 9, aceramic heater 1 is provided as the heating means in a manner to extendin the longitudinal direction.

A reference numeral 12 designates a tube (endless) of heat resistantfilm (fixing film) fitted loosely around the guide stay 9 containing theheater 11.

The guide stay 9 containing the heater 11 is assembled into theapparatus by engaging the extensions 10 and 10 at the opposite left andright ends into the guide grooves 3 and 3 of the left and right sideplates 2 and 2, and sliding them down toward the bottoms of the left andright side plates 2 and 2 of the frame 1. As the guide stays 9 areassembled into the apparatus, the top portion of the pressure roller 4which has been previously assembled and the heater 11 provided at thebottom portion of the guide stay 9 come in contact with each other withthe heat resistant film 12 being interposed.

A reference numeral 13 designates a pressure plate (pressing member)positioned between the top portions of the left and right side plates 2and 2 of the apparatus frame 1, in such a manner as to pivot verticallyabout the rotational axes 14 and 14, and 15 designates a handle(operational member for releasing the pressure) of the pressure plate 13provided on the side opposite to the rotational axis 14.

Reference numerals 16 and 16 designate set springs stretched between thespring hangers 17 and 17 of the pressure plate 13 and the spring hangers18 and 18 of the frame 1, which are provided on the left and rightsides, respectively, and they are positioned on the side opposite to therotational axis 14 of the pressure plate 13.

Therefore, the pressure plate 13 is pulled down by the tension of theset springs 16 and 16 in a manner so as to pivot about the rotationalaxes 14 and 14, up to a point where it comes into contact with stoppers19 and 19 constituting the upper ends of the left and right side plates2 and 2, and is held there.

The pressure plate 13 can be pivoted upward, away from the upper ends ofthe left and right side plates 2 and 2, in a manner so as to rotateabout the rotational axes 14 and 14 by grasping and pulling up thehandle 15 of the pressure plate 13 against the tension of the setsprings 16 and 16, as shown by the solid line in FIG. 1(b).

Reference numerals 20 and 20 designate left and right auxiliary pressuregenerating members. Each of the auxiliary pressure generating members 20and 20 is positioned between the rotational axis 14 and the set spring16. The auxiliary pressure generating member 20 is vertically extendingrod-like member comprising a shaft portion 20a fitted loosely in a hole13a bored in the pressure plate 13 and stoppers 20b and 20c formedintegrally at the top and bottom portions of the shaft portion 20a,wherein the diameters of the stoppers 20b and 20c are larger than thatof the hole 13a.

Reference numerals 21 and 21 designate left and right pressuregenerating springs (compression coil spring), being fitted looselyaround the shaft portions 20a of the auxiliary pressure generatingmember 20 and compressed (to give an auxiliary pressure) between thepressure plate 13 and bottom stopper 22c.

The left and right bottom stoppers 22c and 22c of the auxiliary pressuregenerating member 20 are in contact with the respective extensions ofthe internal film guide stay 9, and when the positional relation betweenthe pressure plate 13 and the frame is such that the pressure plate 13is in contact with the stopper 19 due to the tension of the set spring16 as shown in FIGS. 2 to 4, the bottom stopper 20c of the auxiliarypressure generating member 20 is in contact with the extension 10 of theguide stay 9; thus, expansive force of the pressure generating spring 21presses down the auxiliary pressure generating member 20, which in turnpresses down the guide stay 9. As the guide stay 9 is pressed down, apressure is generated between the guide stay 9 and pressure roller 4with the heat resistant film 12 being interposed; as a result, the beatresistant rubber material layer 6 of the pressure roller 4 is deformed,creating a fixing nip N having a predetermined width in which thesurface of the pressure roller 4 conforms to the surface of the heater11, with the heat resistant film 12 being interposed. Reference numerals10a and 10a designate the portions of the guide stay extensions wherethe bottom stoppers 20c and 20c of the auxiliary pressure generatingmember 20 and 20 contact the guide stay 9.

Hereinafter, the state illustrated in FIG. 1(a) and FIGS. 2 to 4 will becalled the pressure generating state. In this pressure generating state,a gap a is present between the bottom surface of the upper stopper 20bof the auxiliary pressure generating member and the upper surface of thepressure plate 13; thus, the upper stopper 20b of the auxiliary pressuregenerating member and the pressure plate 13 are not engaged; therefore,the auxiliary pressure generating member 20 itself is not subjected tothe tensile stress of the pressure generating spring 21.

Also in the pressure generating state, the set spring 16 must generate atensile force strong enough for holding stably the positional relationbetween the pressure plate 13 and frame 1 after pulling down thepressure plate 13 to the stopper 19, the uppermost portion of the sideplate 2. However, when the illustrated moment is taken intoconsideration, the force generated by the set spring 16 need only belarger than substantially half the force generated by the compressionspring 21. Further, the guide stay 9 and pressure roller 4 are stablypressed to each other with a predetermined contact pressure generated bya predetermined amount of the compressive displacement of the pressuregenerating spring 21.

In the apparatus of this embodiment, the auxiliary pressure generatingmember 20, pressure generating spring 21, rotational axis 14 of thepressure plate, and set spring 16 are provided at each of the front andrear sides of the apparatus so that the pressure applied to the sheetfed into the apparatus becomes uniform across the sheet.

A reference numeral 22 designates a sheet guide attached to theapparatus frame 1; 23, a post-fixation top guide attached to the bottomguide attached to the bottom surface of the pressure plate 13. Each ofthese members extends in the direction perpendicular to this page, thatis, the front to rear direction of FIG. 2, across the width of the sheetfed into the apparatus.

A reference numeral 25 designates a power supply connector for theheater 11. As the power is supplied to the heater 11 through thisconnector 25, the heater 11 generates heat. The temperature of theheater 11 is controlled at a predetermined one by an unshown temperaturecontrol system.

The gear 8 affixed to one end of the pressure roller 4 is engaged withthe gear (unshown) of the driving system provided in the main assemblyof the image forming apparatus, and as it is rotated in thecounterclockwise direction in FIG. 2 at a predetermined peripheralvelocity, the tube of film 12 is rotated around the internal film guidestay 9 because of the surface friction between the pressure roller 4 andthe film 12, sliding on the surface of the heater 11 while maintainingfirm contact with the surface.

While the film 12 is rotated by the rotation of the pressure roller 4and the heater 11 is generating the heat, a sheet material P carrying anunfixed toner image on its upper surface is delivered from an unshownprocessing means for image formation and is introduced by the sheetmaterial guiding member 22 into the fixing nip N, between the rotatingfilm 12 and pressure roller 4.

The sheet material P introduced into the fixing nip N is passed throughthe fixing nip N, together with the film 12, while remaining firmly incontact with the surface of the rotating film 12, and as the sheetmaterial P passes through the fixing nip N, the thermal energy from theheater 11 is transmitted to the sheet material P through the film 12,whereby the toner image is thermally fixed onto the sheet material P.

When the pressure generated in the fixing N needs to be released inorder to take core of the jam or the like problem, the handle 15 of thepressure plate 13 is grasped and pulled up against the tension of theset springs 16 and 16, away from the top edge of the side plate 2 of theframe 1 to the position indicated by the solid line in FIG. 1(b), in amanner so as to pivot about the rotational axis 14.

As the pressure plate 13 rotates upward in this manner, the uppersurface of the pressure plate 13 becomes engaged with the bottom surfaceof the upper stopper 22 of the auxiliary pressure generating member 20at the beginning of the rotation, and then, as the upward rotation ofthe pressure plate 13 continues, the auxiliary pressure generatingmember 20 is pulled upward together with the pressure plate as a result,the bottom stopper 20c of the auxiliary pressure generating member 20becomes separated from the extension 10 of the internal film guide stay9, neutralizing thereby the compressive force of the pressure generatingspring 21 working on the extension 10. In this manner, the pressuregenerated in the fixing nip N, is released, freeing the internal filmguide stay 9 and pressure roller 4 from being pressed to each other andeffecting a state in which the guide stay 9 merely sits on the pressureroller 4, imparting only the self weight upon the pressure roller 4;therefore, the sheet material having been seized in the fixing nip N isloosened to simplify the jam handling operation.

In FIG. 1(a), when L is the distance between the rotational axis 14 ofthe pressure plate 13 and the pressure generating spring 21; 2L, thedistance between the rotational axis 14 of the pressure plate 13 and thespring hanger 17; 3L, the distance between the rotational axis 14 of thepressure plate 13 and the handle 15; and P is the pressure generated inthe fixing nip N by the pressure generating spring 21, the force fneeded by the set spring 16 must satisfy:

    2Lf≧PL; therefore, f≧P/2

The force F necessary for releasing the pressure generated in the fixingnip N must satisfy:

    3LF≧2Lf=LP; therefore, F≧P/3

In other words, the force F required of a use for lifting the handle 15does not need to be large; it is sufficient as long as it is larger than1/3 of the pressure generated in the fixing nip N. Therefore, the handlecan be operated with use of relatively small force.

Generally speaking, the pressure for a small fixing apparatus is 5 to 6kg, and in this case, it is evident that the force required of the useris substantially 2 kg. When the pressure is as large as 10 to 20 kg, allthat is necessary is to design the handle to be such that the leveragefor releasing the pressure becomes larger, or an additional levermechanism may be provided.

After the jam is handled, the pressure plate 13, having been rotatedupward, is lowered to rest on the frame 1, whereby the apparatus in thestate illustrated in FIG. 1(b) regains the state illustrated in FIG.1(a), that is, the pressure generating state.

In this embodiment, since the guide stay 9 and pressure roller 4 arepressed to each other with the use of the pressure generating spring(compression coil spring) 21, the highly precise compression force suchas that in the prior apparatus can be reliably obtained; since thepressure generating spring 21 is held on the pressure plate 13, in acompressed state with use of the auxiliary pressure generating member20, the pressure generating spring 21 can be handled as a part of anassembled unit, improving thereby the assembly efficiency. Also, thedistance by which the pressure plate must be displaced for releasing thepressure can be reduced: since the pressure plate 13 is rotativelysupported by the apparatus frame, the force holding down the pressureplate can be reduced, and in addition, the force necessary for releasingthe pressure can be further reduced because of the component arrangementaccording to this embodiment.

Embodiment 2 (FIGS. 5 and 6)

In Embodiment 1 described hereinbefore, the auxiliary pressuregenerating members 20 and 20 and the internal film guide stay 9 areseparate components, but in this embodiment, the auxiliary pressuregenerating members 20 and 20 and the guide stay 9 are connected to eachother at the bottom of the auxiliary pressure generating member 20.Reference numerals 10b and 10b designate where they are connected.

The compression state of the apparatus is created in the same manner asin the first embodiment. In this embodiment, in order to release thepressure generated in the fixing nip N, the pressure plate 13 is pulledup against the tension of the set springs 16 and 16 in a manner so as torotate about the rotational axes 14 and 14, whereby both the auxiliarypressure generating member 20 and guide stay 9 are pulled up as shown inFIG. 5(b) because the auxiliary pressure generating member 20 and guidestay 9 are connected; thus, creating a gapβ between the pressure roller4 and film 12, where the fixing nip N was present. Therefore, the sheetmaterial seized in the fixing nip N is completely freed, allowing thejam to be more efficiently handled.

The auxiliary pressure generating members 20 and 20 are illustrated asintegrated portions of the guide stay 9, but in light of the componentperformance or its assembly efficiency, they do not need to be connectedor integrated in this manner; the auxiliary pressure generating member20 may be differently combined as long as the combination allows boththe guide stay 9 and pressure plate 13 to be displaced together, withthe auxiliary compressive force of the pressure generating spring 21remaining on the auxiliary pressure generating member.

Embodiment 3 (FIG. 7)

This embodiment is an embodiment of the heat roller type apparatus.

A reference numeral 31 designates an apparatus frame. A referencenumeral 32 designates a heat roller as the heating means made ofaluminum pipe and is rotatively supported between the left and rightside plates 33 and 33 of the frame 31 through C-shaped bearings 34 and34.

A reference numeral 35 designates a halogen heater which is extendedthrough the heat roller 32 and is supported between the left and rightside plates 33 and 33 of the frame 31. The heat roller 32 is heated bythis halogen heater 35, the temperature of which is controlled at apredetermined one by an unshown temperature control system.

A reference numeral 36 designates a pressure plate connected to theframe 31 with use of rotational axes 37 and 37, whereby it can berotated downward away from the frame 31 about these axes 37 and 37.

In each of the left and right side plates 38 and 38 of the pressureplate 36, a vertical guide groove 39, which is symmetrical to the one onthe other side, is provided,in which a bearing 40 is engaged. Thebearing 40 is vertically movable in the guide groove 39.

A reference numeral 40 designates a pressure roller as the opposingmeans which comprises a metallic rod 42 and a heat resistant rubbermaterial layer 43 and is rotatively supported at both left and rightends by left and right bearings 40 and 40.

Reference numerals 44 and 44 designate shaft rods of the auxiliarypressure generating members constructed integrally with the left andright bearings 40 and 40, on the bottom surfaces. The bottom end of eachof the shaft rods is put through the hole 36a of the bottom plate of thepressure plate 36, so that is slightly projects out of the bottom plate,and a stopper 44a is attached to this projecting end. The diameter ofthe hole 36a is made larger than that of the shaft rod, but the diameterof the stopper 44a is made larger than that of the hole 36a.

Reference numerals 45 and 45 designate pressure generating springs(compression spring) which are loosely fitted around the left and rightshaft rods 44 and 44 of the auxiliary pressure generating members, andare compressed between the bearings 40 and 40 and the bottom plate ofthe pressure plate 36.

Reference numerals 46 and 46 designate set springs provided on the sideopposite to the rotational axes of the pressure plate 36, on the leftand right sides of the apparatus, and they are stretched between springhangers 47 and 47 of the pressure plate 31 side and spring hangers 48and 48 of the frame 31 side.

A reference numeral 49 designates a handle (operational member forreleasing the pressure); 50 and 51, a sheet material guide and apost-fixation bottom guide, respectively, both of which are attached tothe pressure plate 36: and 52 designates a post-fixation top guideattached to the frame 31.

When left alone, the positional relation between the pressure plate 36and frame 31 remains in such a state as shown in FIG. 7(a), in which thepressure plate 36 rests on unshown stoppers while being pulled by thetension of the set springs 46 and 46 in a manner so as to rotate aboutthe rotational axes 37 and 37 and close on the frame 31.

In this state, the left and right bearings 40 and 40 are pushed upwardalong the guide grooves 39 and 39 by the auxiliary pressure generatingmembers 44 and 44 imparted with the expansive pressure of the pressuregenerating springs 45 and 45; therefore, the pressure roller 41 ispressed on the bottom surface of the heat roller 32 with a predeterminedcontact pressure. As a result, the heat resistant rubber material layer42 of the pressure roller 41 is deformed; in other words, the surface ofthe pressure roller 41 conforms to the contour of the heat roller 42,creating a fixing nip N having a predetermined width. The apparatusmaintains the pressure generating state in this manner.

The heat roller 32 is rotated by an unshown driving system in theclockwise direction at a predetermined peripheral velocity, and thepressure roller 41 is rotated by the rotation of the heat roller 32.

In a state in which the heat roller 32 has been heated to apredetermined temperature and is being rotated, a sheet material Pcarrying an unfixed toner image on the upper surface is delivered froman unshown processing means for image formation, and is introduced asthe member to be heated into the fixing nip N by the guide 50, and whileit is sandwiched in the nip N and passed through it, the toner image isthermally fixed.

When the pressure generated in the fixing nip N needs to be released inorder to take care of the jam, all that is needed is to grasp the handle49 of the pressure plate 36 and push it down against the tension of theset springs 46 away from the frame 31 to the position indicated by thesolid line in FIG. 7(b), in a manner to rotate about the rotational axes37 and 37.

As the pressure plate 36 is pivoted downward in this manner, the bottomplate of the pressure plate 36 becomes engaged with each of the bottomstoppers 44a and 44a of the respective left and right auxiliary pressuregenerating members 44 and 44 at the beginning of the downward movement,and then, as the downward rotation of the pressure plate 36 iscontinued, the auxiliary pressure generating members 44 and 44, that is,the bearings 40 and 40 and the pressure roller 41, are pushed down,together with the pressure plate 36, away from the frame 31 as shown inFIG. 1(b); thus, the force pressing the heat roller 32 and pressureroller 41 to each other, that is the pressure generated in the fixingnip N, is released.

The relations among the pressure generated by the pressure generatingsprings 45 and 45, the tension generated by the set springs 46 and 46,and the force necessary for operating the handle to release the pressureis the same as that in the first embodiment.

After the jam is taken care of, the apparatus in the state shown in FIG.7(b) returns to the state shown in FIG. 7(a), as the pressure plate 36having been rotated in the opening direction is let rotate in theclosing direction to come to rest on the frame 31.

As described hereinbefore, in the heating apparatus according to thepresent invention, in which the material to be heated is heated by beingsandwiched between the heating means and opposing means which arepressed to each other by the pressing member, a stable contact pressurecan be obtained between the heating means and opposing means; thepressure can be released with use of the least amount of force and withthe least amount of component displacement in spite of the simplestructure. Therefore, the operational efficiency itself in releasing thepressure during the jam handling operation can be improved.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An image heating apparatus comprising:a firstmember; a second member for forming a nip in cooperation with said firstmember; a first frame for supporting said first member; a second frameconnected to said first frame for rotation about a rotational axis; afirst elastic member having an elastic force for pressing said secondmember toward said first member from said second frame; and a secondelastic member for imparting pressure between said first frame and saidsecond frame to increase the elastic force of said first elastic member,said second elastic member being located at a position away from saidfirst elastic member in a direction away from said rotational axis. 2.An apparatus according to claim 1, wherein said first elastic member andsecond elastic member are spring members.
 3. An apparatus according toclaim 1, further comprising a lever for releasing the pressure betweensaid first elastic member and said second elastic member.
 4. Anapparatus according to claim 1, wherein said second member constitutes aheater used in a stationary state, and said heater forms a nip incooperation with said first member, with a film which moves with arecording material being interposed.
 5. An image heating apparatuscomprising:a first member; a second member for forming a nip incooperation with said first member; a first frame for supporting saidfirst member; a second frame connected to said first frame for rotationabout a rotational axis; a first elastic member for pressing said secondmember toward said first member from said second frame; a second elasticmember for imparting pressure between said first frame and said secondframe to increase elastic force of said first elastic member; and alever for releasing the pressure between said first elastic member andsaid second elastic member, said lever being located at a position awayfrom said second elastic member in a direction away from said rotationalaxis.
 6. An apparatus according to claim 5, wherein said second elasticmember is located across said first elastic member from said rotationalaxis.
 7. An apparatus according to claim 5, wherein said first elasticmember and second elastic member are spring members.
 8. An apparatusaccording to claim 5, wherein said second member constitutes a heaterused in a stationary state, and said heater forms a nip in cooperationwith said first member, with a film which moves with a recordingmaterial being interposed.
 9. An image heating apparatus comprising:afirst member; a second member for forming a nip in cooperation with saidfirst member; a first frame for supporting said first member; a secondframe connected to said first frame for rotation about a rotationalaxis; a first elastic member for pressing said second member toward saidfirst member from said second frame; and a second elastic member forimparting pressure between said first frame and said second frame. 10.An apparatus according to claim 9, wherein said first elastic member andsecond elastic member are spring members.
 11. An apparatus according toclaim 9, wherein said second member constitutes a heater used in astationary state, and said heater forms a nip in cooperation with saidfirst member, with a film which moves with a recording material beinginterposed.
 12. An apparatus according to claim 1, 5, or 9, wherein saidsecond frame is contacted to said first elastic member to bear againstelastic force.
 13. An apparatus according to claim 1, 5, or 9, whereinsaid first frame is fixed.
 14. An apparatus according to claim 4, 8, or11, wherein said first member includes a roller.
 15. An apparatusaccording to claim 14, wherein said roller is a driving roller.
 16. Anapparatus according to claim 1, 5, or 9, wherein said first memberincludes a heating roller, and said second member includes a pressingroller.
 17. An apparatus according to claim 1, 5, or 9, wherein arecording material carrying an unfixed image is fed up by said nip, andthe unfixed image is fixed by the feeding through the nip.